Fix to merge code from `_create_table_statement` and `get_schema`

Closes #8097

Reorganized a lot of the SQL schema creation code.  Now database table is not dropped / create when `PandasSQLTable` object is instantiated, but instead when `insert` method is called on it.  This allow us to `get_schema` to generate `CREATE TABLE` code without actually creating the table.
(Includes updates from #8083, so will have to be rebased when that is merged)
you can just use `zip` (it is already imported from pandas.compat at the top of this file)
`zip` return an iterator in python3 by default, that's why `itertools.izip` does not exist anymore.